Butyric acid

Butyric acid

Overview
Butyric acid also known under the systematic name butanoic acid, is a carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

 with the structural formula C
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

H
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

3CH2CH2-COOH. Salts and ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...

s of butyric acid are known as butyrates or butanoates. Butyric acid is found in butter
Butter
Butter is a dairy product made by churning fresh or fermented cream or milk. It is generally used as a spread and a condiment, as well as in cooking applications, such as baking, sauce making, and pan frying...

, parmesan cheese, and vomit, and as a product of anaerobic fermentation (including in the colon
Colon (anatomy)
The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...

 and as body odor
Body odor
Body odor or body odour, sometimes colloquially abbreviated as B.O., is the smell of bacteria growing on the body. The bacteria multiply rapidly in the presence of sweat, but sweat itself is almost completely odorless to humans....

). It has an unpleasant smell
Odor
An odor or odour is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. Odors are also commonly called scents, which can refer to both pleasant and unpleasant odors...

 and acrid taste
Taste
Taste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....

, with a sweetish aftertaste (similar to ether
Diethyl ether
Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor...

).
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Encyclopedia
Butyric acid also known under the systematic name butanoic acid, is a carboxylic acid
Carboxylic acid
Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

 with the structural formula C
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

H
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

3CH2CH2-COOH. Salts and ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...

s of butyric acid are known as butyrates or butanoates. Butyric acid is found in butter
Butter
Butter is a dairy product made by churning fresh or fermented cream or milk. It is generally used as a spread and a condiment, as well as in cooking applications, such as baking, sauce making, and pan frying...

, parmesan cheese, and vomit, and as a product of anaerobic fermentation (including in the colon
Colon (anatomy)
The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...

 and as body odor
Body odor
Body odor or body odour, sometimes colloquially abbreviated as B.O., is the smell of bacteria growing on the body. The bacteria multiply rapidly in the presence of sweat, but sweat itself is almost completely odorless to humans....

). It has an unpleasant smell
Odor
An odor or odour is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. Odors are also commonly called scents, which can refer to both pleasant and unpleasant odors...

 and acrid taste
Taste
Taste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....

, with a sweetish aftertaste (similar to ether
Diethyl ether
Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor...

). It can be detected by mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s with good scent detection abilities (such as dog
Dog
The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...

s) at 10 ppb
PPB
PPB can stand for:* Party political broadcast, a type of political programming in the United Kingdom* parts-per-billion, a unit of concentration* Portland Police Bureau, a police agency for the city of Portland...

, whereas human
Human
Humans are the only living species in the Homo genus...

s can detect it in concentrations above 10 ppm.

Chemistry


Butyric acid is a fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...

 occurring in the form of esters in animal fats and plant oils. The triglyceride
Glyceride
Glycerides, more correctly known as acylglycerols, are esters formed from glycerol and fatty acids.Glycerol has three hydroxyl functional groups, which can be esterified with one, two, or three fatty acids to form monoglycerides, diglycerides, and triglycerides.Vegetable oils and animal fats...

 of butyric acid makes up 3% to 4% of butter. When butter goes rancid, butyric acid is liberated from the glyceride by hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...

 leading to the unpleasant odor. It is an important member of the fatty acid sub-group called short-chain fatty acids. Butyric acid is a weak acid
Weak acid
A weak acid is an acid that dissociates incompletely. It does not release all of its hydrogens in a solution, donating only a partial amount of its protons to the solution...

 with a pKa
PKA
PKA, pKa, or other similar variations may stand for:* pKa, the symbol for the acid dissociation constant at logarithmic scale* Protein kinase A, a class of cAMP-dependent enzymes* Pi Kappa Alpha, the North-American social fraternity...

 of 4.82, similar to acetic acid
Acetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...

, which has pKa 4.76. The similar strength of these acids results from their common -CH2COOH terminal structure. Pure butyric acid is 10.9 molar.

The acid is an oily colorless liquid that is easily soluble in water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

, ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

, and ether
Ether
Ethers are a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R'. A typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether"...

, and can be separated from an aqueous phase by saturation with salts such as calcium chloride
Calcium chloride
Calcium chloride, CaCl2, is a salt of calcium and chlorine. It behaves as a typical ionic halide, and is solid at room temperature. Common applications include brine for refrigeration plants, ice and dust control on roads, and desiccation...

. Potassium dichromate and sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

 oxidize it to carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 and acetic acid
Acetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...

, while alkaline potassium permanganate
Potassium permanganate
Potassium permanganate is an inorganic chemical compound with the formula KMnO4. It is a salt consisting of K+ and MnO4− ions. Formerly known as permanganate of potash or Condy's crystals, it is a strong oxidizing agent. It dissolves in water to give intensely purple solutions, the...

 oxidizes it to carbon dioxide. The calcium salt, Ca(C4H7O2)2·H2O, is less soluble in hot water than in cold.

Butyric acid has a structural isomer called isobutyric acid
Isobutyric acid
Isobutyric acid, also known as 2-methylpropanoic acid, is a carboxylic acid with structural formula 2-CH-COOH. It is found in the free state in carobs and in the root of Arnica dulcis, and as an ethyl ester in croton oil....

 (2-methylpropanoic acid).

Production


It is industrially prepared by the fermentation of sugar
Sugar
Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...

 or starch
Starch
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...

, brought about by the addition of putrefying cheese
Cheese
Cheese is a generic term for a diverse group of milk-based food products. Cheese is produced throughout the world in wide-ranging flavors, textures, and forms....

, with calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...

 added to neutralize the acids formed in the process. The butyric fermentation of starch is aided by the direct addition of Bacillus subtilis
Bacillus subtilis
Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium commonly found in soil. A member of the genus Bacillus, B. subtilis is rod-shaped, and has the ability to form a tough, protective endospore, allowing the organism to tolerate...

. Salts and esters of the acid are called butyrate
Butyrate
Butyrate is the traditional name for the conjugate base of butanoic acid . The formula of the butanoate ion is C4H7O2-. The archaic name is used as part of the name of butyrates or butanoates, or esters and salts of butyric acid, a short chain fatty acid...

s or butanoates.

Butyric acid or fermentation butyric acid is also found as a hexyl ester
Ester
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...

 hexyl butyrate in the oil of Heracleum giganteum (a type of hogweed) and as the octyl ester octyl butyrate in parsnip
Parsnip
The parsnip is a root vegetable related to the carrot. Parsnips resemble carrots, but are paler than most carrots and have a sweeter taste, especially when cooked. The buttery, slightly spicy, sweet flavor of cooked mature parsnips is reminiscent of butterscotch, honey, and subtle cardamom...

 (Pastinaca sativa); it has also been noticed in the fluors of the flesh and in perspiration.

Uses


Butyric acid is used in the preparation of various butyrate esters. Low-molecular-weight esters of butyric acid, such as methyl butyrate
Methyl butyrate
Methyl butyrate, also known under the systematic name methyl butanoate, is the methyl ester of butyric acid. Like most esters, it has a fruity odour, in this case resembling apples or pineapples. At room temperature, it is a colourless liquid with low solubility in water, upon which it floats to...

, have mostly pleasant aromas or tastes. As a consequence, they find use as food and perfume additives. It is also used as an animal feed supplement, due to the ability to reduce pathogenic bacterial colonisation. It is an approved food flavouring in the EU FLAVIS database (number 08.005).

Due to its powerful odor, it has also been used as a fishing bait additive. Many of the commercially available flavours used in carp
Common carp
The Common carp is a widespread freshwater fish of eutrophic waters in lakes and large rivers in Europe and Asia. The wild populations are considered vulnerable to extinction, but the species has also been domesticated and introduced into environments worldwide, and is often considered an invasive...

 (Cyprinus carpio) baits use butyric acid as their ester base; however, it is not clear whether fish are attracted by the butyric acid itself or the additional substances added to it. Butyric acid was, however, one of the few organic acids shown to be palatable for both tench
Tench
The tench or doctor fish is a freshwater and brackish water fish of the cyprinid family found throughout Eurasia from Western Europe including the British Isles east into Asia as far as the Ob and Yenisei Rivers. It is also found in Lake Baikal...

 and bitterling
Bitterling
The Amur Bitterling, Rhodeus sericeus, is a small fish of the carp family. It is sometimes just called "bitterling", but this is wrong: for one thing, it dates back to the time when the European Bitterling was still considered conspecific with R. sericeus, for another, "bitterling" properly refers...

.

The substance has also been used as a noxious, nausea-inducing repellent by anti-whaling protesters to disrupt Japanese whaling crews, as well as by anti-abortion protesters to disrupt abortion clinics.

Biosynthesis


Butyrate is produced as end-product of a fermentation process solely performed by obligate
Obligate
Obligate means "by necessity" and is used mainly in biology in phrases such as:* Obligate aerobe, an organism that cannot survive without oxygen* Obligate anaerobe, an organism that cannot survive in the presence of oxygen...

 anaerobic
Anaerobic organism
An anaerobic organism or anaerobe is any organism that does not require oxygen for growth. It could possibly react negatively and may even die if oxygen is present...

 bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

. Fermented Kombucha
Kombucha
Kombucha is an effervescent tea-based beverage that is often drunk for its anecdotal health benefits or medicinal purposes. Kombucha is available commercially and can be made at home by fermenting tea using a visible, solid mass of yeast and bacteria which forms the kombucha culture, often referred...

 "tea" includes butyric acid as a result of the fermentation. This fermentation pathway was discovered by Louis Pasteur
Louis Pasteur
Louis Pasteur was a French chemist and microbiologist born in Dole. He is remembered for his remarkable breakthroughs in the causes and preventions of diseases. His discoveries reduced mortality from puerperal fever, and he created the first vaccine for rabies and anthrax. His experiments...

 in 1861. Examples of butyrate-producing species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of bacteria:
  • Clostridium acetobutylicum
    Clostridium acetobutylicum
    Clostridium acetobutylicum, ATCC 824, is included in the genus Clostridium, is a commercially valuable bacterium sometimes called the "Weizmann Organism", after Jewish-Russian born Chaim Weizmann, then senior lecturer at the University of Manchester, England, used them in 1916 as a bio-chemical...

  • Clostridium butyricum
    Clostridium butyricum
    Clostridium butyricum is an anaerobic prokaryote that requires the absolute absence of oxygen to grow. It produces butyric acid which is an indicator of the presence of saccharolytic clostridia. It is an endospore-former and can live under rough conditions...

  • Clostridium kluyveri
    Clostridium kluyveri
    Clostridium kluyveri is an anaerobic, motile, gram-positive bacterium....

  • Clostridium pasteurianum
  • Fusobacterium nucleatum
    Fusobacterium nucleatum
    Fusobacterium nucleatum is an oral bacterium, indigenous to the human oral cavity, that plays a role in periodontal disease. This organism is commonly recovered from different monomicrobial and mixed infections in humans and animals...

  • Butyrivibrio fibrisolvens
  • Eubacterium limosum


The pathway starts with the glycolytic
Glycolysis
Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+...

 cleavage of glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...

 to two molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

s of pyruvate, as happens in most organisms. Pyruvate is then oxidized into acetyl coenzyme A using a unique mechanism that involves an enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 system called pyruvate-ferredoxin oxidoreductase. Two molecules of carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 (CO2) and two molecules of elemental hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 (H2) are formed as wastes products from the cell. Then,
ActionResponsible enzyme
Acetyl coenzyme A converts into acetoacetyl coenzyme A  acetyl-CoA-acetyl transferase
Acetoacetyl coenzyme A converts into β-hydroxybutyryl CoA  β-hydroxybutyryl-CoA dehydrogenase
β-hydroxybutyryl CoA converts into crotonyl CoA  crotonase
Crotonyl CoA converts into butyryl CoA (CH3CH2CH2C=O-CoA) butyryl CoA dehydrogenase
Butyryl CoA dehydrogenase
Butyryl CoA dehydrogenase is a flavoprotein.It acts upon butyryl-coenzyme A....

A phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...

 group replaces CoA to form butyryl phosphate
Butyryl phosphate
Butyryl phosphate is an intermediate in the fermentation of butyric acid....

 
phosphobutyrylase
The phosphate group joins ADP
Adenosine diphosphate
Adenosine diphosphate, abbreviated ADP, is a nucleoside diphosphate. It is an ester of pyrophosphoric acid with the nucleoside adenosine. ADP consists of the pyrophosphate group, the pentose sugar ribose, and the nucleobase adenine....

 to form ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...

 and butyrate
Butyrate
Butyrate is the traditional name for the conjugate base of butanoic acid . The formula of the butanoate ion is C4H7O2-. The archaic name is used as part of the name of butyrates or butanoates, or esters and salts of butyric acid, a short chain fatty acid...

 
butyrate kinase
Butyrate kinase
In enzymology, a butyrate kinase is an enzyme that catalyzes the chemical reactionThus, the two substrates of this enzyme are ATP and butanoate, whereas its two products are ADP and butanoyl phosphate....



ATP is produced, as can be seen, in the last step of the fermentation. Three molecules of ATP are produced for each glucose molecule, a relatively high yield. The balanced equation for this fermentation is
C6H12O6 → C4H8O2 + 2CO2 + 2H2.


Several species form acetone
Acetone
Acetone is the organic compound with the formula 2CO, a colorless, mobile, flammable liquid, the simplest example of the ketones.Acetone is miscible with water and serves as an important solvent in its own right, typically as the solvent of choice for cleaning purposes in the laboratory...

 and n-butanol
N-Butanol
n-Butanol or n-butyl alcohol or normal butanol is a primary alcohol with a 4-carbon structure and the molecular formula C4H9OH. Its isomers include isobutanol, 2-butanol, and tert-butanol...

 in an alternative pathway, which starts as butyrate fermentation. Some of these species are:
  • Clostridium acetobutylicum
    Clostridium acetobutylicum
    Clostridium acetobutylicum, ATCC 824, is included in the genus Clostridium, is a commercially valuable bacterium sometimes called the "Weizmann Organism", after Jewish-Russian born Chaim Weizmann, then senior lecturer at the University of Manchester, England, used them in 1916 as a bio-chemical...

    , the most prominent acetone and butanol producer, used also in industry
  • Clostridium beijerinckii
    Clostridium beijerinckii
    Clostridium beijerinckii is a gram positive, rod shaped, motile bacterium of the genus Clostridium. It has been isolated from feces and soil...

  • Clostridium tetanomorphum
  • Clostridium aurantibutyricum.


These bacteria begin with butyrate fermentation, as described above, but, when the pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 drops below 5, they switch into butanol and acetone production in order to prevent further lowering of the pH. Two molecules of butanol are formed for each molecule of acetone.

The change in the pathway occurs after acetoacetyl CoA formation. This intermediate then takes two possible pathways:
  • acetoacetyl CoA → acetoacetate → acetone
  • acetoacetyl CoA → butyryl CoA → butanal
    Butanal
    Butyraldehyde, also known as butanal, is an organic compound with the formula CH32CHO. This compound is the aldehyde derivative of butane. It is a colourless flammable liquid with an acrid smell...

     → butanol


Highly-fermentable fiber residues, such as those from resistant starch
Resistant starch
Resistant starch is starch and starch degradation products that escape digestion in the small intestine of healthy individuals. Resistant starch is considered the third type of dietary fiber, as it can deliver some of the benefits of insoluble fiber and some of the benefits of soluble fiber.Some...

, oat bran, pectin
Pectin
Pectin is a structural heteropolysaccharide contained in the primary cell walls of terrestrial plants. It was first isolated and described in 1825 by Henri Braconnot...

, and guar
Guar
The guar/guwar/guvar bean or cluster bean is an annual legume and the source of guar gum. It grows best under conditions with frequent rainfall, but tolerates arid conditions well. About 80% of world production occurs in India, but, due to strong demand, the plant is being introduced into new areas...

 are transformed by colonic bacteria
Gut flora
Gut flora consists of microorganisms that live in the digestive tracts of animals and is the largest reservoir of human flora. In this context, gut is synonymous with intestinal, and flora with microbiota and microflora....

 into short-chain fatty acids (SCFA) including butyrate, producing more SCFA than less fermentable fibers such as cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....

s. One study found that resistant starch consistently produces more butyrate than other types of dietary fiber
Dietary fiber
Dietary fiber, dietary fibre, or sometimes roughage is the indigestible portion of plant foods having two main components:* soluble fiber that is readily fermented in the colon into gases and physiologically active byproducts, and* insoluble fiber that is metabolically inert, absorbing water as it...

. The production of SCFA from fibers in ruminant
Ruminant
A ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...

 animals such as cattle is responsible for the butyrate content of milk and butter.

Cancer and life span


The role of butyrate changes differs between normal and cancerous cells. This is known as the "butyrate paradox". Butyrate inhibits colonic tumor cells, and promotes healthy colonic epithelial cells; but the signaling mechanism is not well understood. A review suggested that the chemopreventive benefits of butyrate depend in part on amount, time of exposure with respect to the tumorigenic process, and the type of fat in the diet. The production of volatile fatty acids
Volatile fatty acids
Volatile fatty acids are fatty acids with a carbon chain of six carbons or fewer. They are now usually referred to as short-chain fatty acids .They can be created through fermentation in the intestine.Examples include:* Acetic acid...

 such as butyrate from fermentable fibers may contribute to the role of dietary fiber in colon cancer.

Butyric acid can act as an HDAC inhibitor, inhibiting the function of histone deacetylase
Histone deacetylase
Histone deacetylases are a class of enzymes that remove acetyl groups from an ε-N-acetyl lysine amino acid on a histone. This is important because DNA is wrapped around histones, and DNA expression is regulated by acetylation and de-acetylation. Its action is opposite to that of histone...

 enzymes, thereby favoring an acetylated state of histone
Histone
In biology, histones are highly alkaline proteins found in eukaryotic cell nuclei that package and order the DNA into structural units called nucleosomes. They are the chief protein components of chromatin, acting as spools around which DNA winds, and play a role in gene regulation...

s in the cell. Acetylated histones have a lower affinity for DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 than non-acetylated histones, due to the neutralization of electrostatic charge interactions. In general, it is thought that transcription factors will be unable to access regions where histones are tightly associated with DNA (i.e., non-acetylated, e.g., heterochromatin). Therefore, it is thought that butyric acid enhances the transcriptional activity at promoters, which are typically silenced or downregulated due to histone deacetylase activity.

Two HDAC inhibitors, sodium butyrate
Sodium butyrate
Sodium butyrate is a compound with formula Na. It is the sodium salt of butyric acid. It has various effects on cultured mammalian cells including inhibition of proliferation, induction of differentiation and induction or repression of gene expression. As such, it can be used in lab to bring about...

 (NaB) and trichostatin A
Trichostatin A
Trichostatin A is an organic compound that serves as an antifungal antibiotic and selectively inhibits the class I and II mammalian histone deacetylase families of enzymes, but not class III HDACs . TSA inhibits the eukaryotic cell cycle during the beginning of the growth stage...

 (TSA), increase lifespan in experimental animals.

External links